Wednesday, May 02, 2018

Scottish Scientists Just Made a Contact Lens That Lets You Shoot Lasers from Your Eyes

There's an old one-liner: "Laser eye surgery isn't nearly as cool as it sounds". Now, I don't know if this is fair—in my opinion, blasting a person's cornea back into shape so that they can see without glasses is one of the most awesome applications of laser tech. But as cool as that is, it's still not as cool as a surgery that gives you the ability to shoot lasers from your eyes—something that may be on the horizon thanks to researchers at Scotland's University of St. Andrews.

Right off the bat, I want to be clear: this isn't one of those "Scientists Develop Real Working Lightsaber!" stories, where it turns out that all they've really done is demonstrate photon coupling in rubidium gas or something. The team at St. Andrews:

  1. made an ultrathin membrane laser, using a pretty revolutionary new technique
  2. mounted it on a contact lens
  3. put the lens on a disembodied cow eye
...and now the eye shoots laser beams when you shine the right kind of light at it.

Hopefully they find a way to power it without shining a blinding light at your own eye...
but even if they don't, I might still want 'em.
Image Credit: Markus Karl, et al. Nature Communications.
On the list of superpowers that I expected technology to make real in my lifetime, laser vision is pretty far down the list. The components would have to be unbelievably tiny, and powering them would be a real pain in the, uh...eye. But the team at St. Andrews has solved that first problem, using cutting-edge fabrication techniques to develop a new kind of laser that's as slender as the laws of physics allow. Mounting it on a cow's eye seems to be an unusual choice, but the researchers wanted to demonstrate its potential applications in security—where they say laser-enhanced contacts could improve biometric identification.

That's just the beginning, though. Just think: the first laser got called a "solution seeking a problem"—a quote that's often taken out of context. In one sense, it seems shortsighted: a "what good is it?" kind of sentiment. But in truth, it's a statement about the new technology's potential to change the world in ways that we can't even imagine yet, and the same goes for this new device. The scientists who fabricated it have already demonstrated that it's flexible enough to be affixed to dollar bills, contacts, and even a human thumbnail—what other applications could a tiny membrane laser hold?

Though the final product is what's flashy, the real magic here is the manufacturing technique, which strips away everything but the bare bones of what makes a laser. Traditionally, lasers had three parts: a pump source that provides energy (often in the form of light), a gain medium, where that energy is converted into light of a single wavelength, and a waveguide, to steer the energy from the pump to the gain medium and out as a coherent beam.

In my undergrad lab, we worked with a huge bench laser, the heart of which was an elliptical cavity with a gold-coated interior. This cavity—shown below in cross-section (looking down the "barrel" of the laser) is the waveguide—and although the word sounds pretty sci-fi, the concept is actually pretty easy to understand. The shape of the cavity is designed so that any ray of light coming out of the lamp (the pump source) will reflect around the cavity until it ends up in the rod, which is made of a special crystal that serves as the gain medium. Light that ends up in the rod can come back out the sides, but it'll bounce around the cavity some more until it ends up back in the rod; the only escape is out the ends, where—after bouncing back and forth between some reflectors—it becomes a coherent beam of laser light!

Imagine drawing rays leading away from the lamp, and reflecting off the interior walls of the cavity—no matter what angle they initially come off at, they'll end up in the rod.
Maybe my experience with this clunker of a design is the reason I never imagined we'd see anything as remarkable as this invention in my lifetime; the ultrathin new laser is of a different class entirely. While the fluorescent rig above is necessary for some high-power applications, it's practically stone-age compared to more recent laser technology, much of which relies on LEDs as both the pump source and the gain medium; doubling these up is how we get handheld laser pointers.

But those still need a battery and a housing—difficult things to put on a banknote, or in your eye. That's why the new laser is optically pumped—meaning that it works by converting light shined on it externally into laser light using a specially-patterned surface that traps just the right wavelengths of light. That means we won't be seeing dollar bills that shoot lasers on their own, but maybe ones that do so in response to a special anti-counterfeit light.

Most of these technologies aren't breaking news, however—the really remarkable part of this latest paper is that the study's authors demonstrated the ultrathin laser's portability. Usually, lasers of this type still have to be mounted on a special surface made in the lab, which limits their applications. But by layering the waveguide and diode components onto a thin "sacrificial" layer that could then be dissolved away, the St. Andrews team managed to make one of the first free-floating membrane lasers in history.

I mean it literally when I say "free-floating"—once the sacrificial layer dissolves, the laser membrane floats up to the surface of a bath of water, where it can be scooped up and affixed to a wide variety of surfaces.
Image Credit: Markus Karl, et al. Nature Communications.
In the authors' own words, the new laser "...maximizes mechanical flexibility and reduces the thickness of the laser to its ultimate limit, by using an architecture that comprises only the organic semiconductor and a DFB resonator...". Reading this, I was reminded of the words of a famous French author: "...perfection is attained, not when there is nothing more to add, but when there is nothing more to take away."

So is this perfection? Probably not—it seems there's always another level of innovation around the corner—but I think we can all agree that this kind of step toward superpowers is extremely cool.

—Stephen Skolnick

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